Duo Product Security Advisory

Overview

Duo Security has identified an issue in which it is possible to bypass second factor authentication of multisite WordPress deployments which use the Duo WordPress plugin (prior to version 2.0).

Description

In a WordPress deployment using the “multisite” feature, WordPress allows members of different sites in the same network to authenticate through sites they are not a direct member of. In these deployments, if the Duo WordPress plugin is disabled globally -- but enabled on a site-by-site basis -- a member of a 2FA-enabled site may be able to bypass second factor authentication. Consider the following example:

A multisite WordPress deployment has two sites, Site1 and Site2, with the Duo WordPress plugin enabled for Site1 but disabled for Site2. Under normal circumstances, users logging into Site1 will be prompted for primary credentials and second-factor authentication; Site2 users will be prompted only for primary credentials. A Site1 user may force-browse to the login URL of Site2, which will authenticate the user (as part of the same Wordpress multisite network), and redirect them back to Site1, without prompting for second-factor authentication.

Note: This does not apply to single-site blogs.

Impact

A user with valid primary authentication credentials (username and password) may be able to bypass the second factor of authentication.